From 4ed0cebda869315a9e729daa55c50a16e2a5cde1 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 3 May 2011 01:52:13 -0700
Subject: [PATCH] * floatfns.c (Fexpt): Likewise.

---
 src/ChangeLog  |  1 +
 src/floatfns.c | 46 +++++++++++++++++++++++++++++-----------------
 2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 435f90abad9..26b3af3225c 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -7,6 +7,7 @@
 	(arith_driver, Fadd1, Fsub1): Use floating point if the result is
 	out of Emacs fixnum range.
 	* bytecode.c (exec_byte_code): Likewise, for Bsub1, Badd1, Bnegate.
+	* floatfns.c (Fexpt): Likewise.
 
 	* callproc.c (Fcall_process): Use 'volatile' to avoid vfork clobbering.
 
diff --git a/src/floatfns.c b/src/floatfns.c
index 1232fc0afa1..5c286772864 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -491,27 +491,39 @@ DEFUN ("expt", Fexpt, Sexpt, 2, 2, 0,
       y = XINT (arg2);
       acc = 1;
 
-      if (y < 0)
-	{
-	  if (x == 1)
-	    acc = 1;
-	  else if (x == -1)
-	    acc = (y & 1) ? -1 : 1;
-	  else
-	    acc = 0;
-	}
-      else
+      if ((x == 0 && y != 0) || x == 1 || (x == -1 && (y & 1)))
+	return arg1;
+      if (x == -1)
+	y = 0;
+
+      while (1)
 	{
-	  while (y > 0)
+	  if (y & 1)
 	    {
-	      if (y & 1)
-		acc *= x;
-	      x *= x;
-	      y = (unsigned)y >> 1;
+	      if (x < 0
+		  ? (acc < 0
+		     ? acc < MOST_POSITIVE_FIXNUM / x
+		     : MOST_NEGATIVE_FIXNUM / x < acc)
+		  : (acc < 0
+		     ? acc < MOST_NEGATIVE_FIXNUM / x
+		     : MOST_POSITIVE_FIXNUM / x < acc))
+		break;
+	      acc *= x;
 	    }
+
+	  y >>= 1;
+	  if (y == 0)
+	    {
+	      XSETINT (val, acc);
+	      return val;
+	    }
+
+	  if (x < 0
+	      ? x < MOST_POSITIVE_FIXNUM / x
+	      : MOST_POSITIVE_FIXNUM / x < x)
+	    break;
+	  x *= x;
 	}
-      XSETINT (val, acc);
-      return val;
     }
   f1 = FLOATP (arg1) ? XFLOAT_DATA (arg1) : XINT (arg1);
   f2 = FLOATP (arg2) ? XFLOAT_DATA (arg2) : XINT (arg2);
-- 
2.11.4.GIT